Bariatric Surgery Reduces CV Events, Mechanisms Still Unclear

January 03, 2012

January 3, 2012 (Gothenburg, Sweden) — A new analysis of the Swedish Obese Subjects (SOS) study has shown that bariatric surgery led to a 30% reduction in the incidence of cardiovascular events in obese patients compared with those who received usual care and an almost 50% reduction in cardiovascular deaths, following almost 15 years of follow-up [1]. Dr Lars Sjöström (Sahlgrenska University Hospital, Gothenburg, Sweden) and colleagues report their findings in the January 4, 2012 issue of the Journal of the American Medical Association.

"This is very important since no nonsurgical obesity treatments have been able to reduce cardiovascular disease," Sjöström told heartwire . "Bariatric surgery is so far unique in its ability to reduce cardiovascular events. SOS is the only prospective study in this field, but two retrospective bariatric-surgery studies are in agreement with our findings," he added.

Bariatric surgery is so far unique in its ability to reduce cardiovascular events.

But the results also show that neither body-mass index (BMI) at baseline — before the operation — nor weight loss after surgery predicted the surgical benefit with respect to reduced cardiovascular-disease incidence. Baseline insulin concentration was strongly related to future cardiovascular benefit in post hoc analysis, however, with those with a high insulin level having a more favorable outcome.

But it may well take 10 years to dissect out which specific criteria will best predict who gains the most benefit from bariatric surgery, say Sjöström et al.

Survival benefits minimal, surgery not indicated in the healthy obese

In an accompanying editorial [2], Dr Edward H Livingstone (University of Texas Southwestern Medical Center, Dallas), observes that "the benefits from bariatric surgery are not related to weight loss, the main reason these operations are performed." And he notes that although there were significant differences in CV events and deaths between the surgery and nonsurgery groups in these latest SOS data, "the absolute difference between groups was small."

Taken together with the results of other studies in the field, these findings suggest that the clearest potential benefit from obesity surgery — greater survival — "is at best only minimally improved," he observes.

He therefore concludes that obese patients who are otherwise healthy should not have bariatric surgery, because "the expected health benefits do not necessarily exceed the risks of weight-loss operations."

But Sjöström says he does not agree with this conclusion. "For instance, in our paper on overall mortality, published in the New England Journal of Medicine in 2007 [3], we found a highly significant effect on mortality in spite of taking the postoperative mortality (0.25%) into account," he observes.

Need to pinpoint those who can benefit most from bariatric surgery

Sjöström told heartwire that the finding that BMI doesn't predict who will gain CV benefits from bariatric surgery is key, since "all bariatric surgery guidelines are based on BMI. We think that these guidelines need to be modified in such a way that those patients who benefit most can be selected." Livingstone agrees. "BMI alone should not be used as a criterion for obesity treatment or bariatric-surgery operations."

BMI alone should not be used as a criterion for obesity treatment or bariatric surgery operations.

What seems to be of central importance, says Sjöström, is whether patients are operated on or not. "The lack of significant relationships between weight change and risk reduction in the surgery group could be a statistical power issue. Alternatively, changes to things other than weight are more important for the cardiovascular risk reduction. It would be very important to understand such mechanisms because it might be possible to mimic them with nonsurgical methods," he observes.

It is time for the NIH to assess the available evidence and provide updated recommendations for bariatric procedures for the treatment of obesity.

Livingstone told heartwire he believes obese individuals should be considered for bariatric surgery if they have an established severe complication, including diabetes, severe hypertension, or obstructive sleep apnea or are patients with osteoarthritis who need a joint replacement.

And he is urging a scientific reappraisal of the issues involved. "It is time for the [US National Institutes of Health] NIH to convene another expert panel to rigorously assess the available evidence and provide updated recommendations for bariatric procedures for the treatment of obesity," he advises.

Identifying specific subgroups that will benefit from surgery may take 10 years

In their paper, Sjöström et al outline their latest findings from SOS, based on 2010 obese patients who underwent bariatric surgery and 2037 contemporaneously matched control subjects who received usual care, until the end of December 2009, with a median follow-up of 14.7 years. Participants were aged between 37 to 60 years and had to have a BMI of at least 34 in men and at least 38 in women. Those undergoing surgery had gastric bypass (13.7%), banding (18.7%), or vertical banded gastroplasty (68.1%).

The primary end point of SOS — total mortality — was significantly reduced among those undergoing bariatric surgery, as previously reported. MI and stroke events were predefined secondary end points, considered separately and combined.

Bariatric surgery was associated with a reduced number of CV deaths (28 in the surgery group vs 49 in the control group; adjusted hazard ratio 0.47; p=0.002). The number of total first fatal or nonfatal CV events — MI or stroke, whichever came first — was also lower in the surgery group (199 events vs 234; adjusted HR 0.67; p < 0.001).

"Bariatric surgery prevents cardiovascular events," the researchers state. These latest results, "along with our previously reported associations between bariatric surgery and favorable outcomes — regarding long-term changes of body weight, cardiovascular risk factors, quality of life, diabetes, cancer, and mortality — demonstrate that there are many benefits to bariatric surgery, some of which are independent of the degree of the surgically induced weight loss," they observe.

But they say it is too soon to make clinical decisions based on their post hoc analysis — for example, the finding that baseline insulin is a predictor of who will gain the most cardiovascular benefit from bariatric surgery. Such treatment effects will require confirmation in prospective controlled trials in high-risk subgroups specified at baseline, and this may well take "at least 10 years."

In the meantime, clinical decisions "must be based on best evidence available."

Sjöström reports unrestricted SOS grants from Sanofi-Aventis and Johnson & Johnson; receiving lecture and consulting fees from AstraZeneca, Biovitrium, Bristol-Myers Squibb, GlaxoSmithKline, Johnson & Johnson, Lenimen, Merck, Novo Nordisk, Hoffman LaRoche, Sanofi-Aventis, and Servier; and holding stocks in Lenimen and being chair of its board. Disclosures for the coauthors are listed in the paper. Livingstone reports no conflicts of interest.


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